If you live in a cold weather town can you wait until the spring to socialize your puppy? The answer is no. 

There is a lot of research to show that the critical socialization period for puppies ends at 12-18 weeks of age.
What does that mean for you and your puppy?
It means that you need to go out of your way to introduce your dog to every type of person, noise, and event that she will come into contact with – before she reaches 18 weeks of age. 18 weeks is not an absolute, depending on the research that you read, data shows that the critical socialization is up to 12-20 weeks of age.
From my experience, 18-20 weeks of age is the most critical time. What happens if you do not socialize your puppy during this critical socialization period? It means that there is a much higher chance that your dog will be frightened of people, noises, movement, handling or events that she comes into contact with later in life, unless she is comfortable with those stimuli.
One way to think about puppies’ brains is that they are like “little balls of clay†that are being formed with every new experience. Their relationship with the world is formed with each new experience. During this socialization period, they learn what they should be cautious of and also what they like. If they see something for the first time after this period of time, their normal instinctual reaction is to be more cautious.
The example that I use in my private practice is to say, “Your puppy is not afraid of the coffee table because she sees it every day and she knows that it means her no harm.â€â€¨â€¨That is how you should structure your socialization strategy. I want your puppy to "grow up" with everything that will be in her daily world. Ask a simple question. What will my puppy possibly come into contact with for the rest of her life? One important factor to keep in mind is that dogs do not generalize. What this means is that they don’t look at people and say, “I am comfortable with people.â€
They are only comfortable with the races, sizes, and types of people that they have come into contact with. If your puppy only sees tall men with brown hair, she might not be comfortable with small children, for example. Can your puppy have a great experience with one child and be comfortable with children?
Maybe she will, but probably not.
Some breeds are actually easier to socialize than others. Labrador Retrievers and Pugs, for instance, are much less reactive than certain breeds such as German Shepherds. Being more reactive doesn’t make German Shepherds any less wonderful; it is just something to keep in mind. When you are socializing a more reactive dog you need to socialize him even more to ensure he is comfortable with the world around him. With any dog, I recommend that you socialize your puppy as many times as possible to each event that you want her to be comfortable with. Regular, repeated exposures are critical for your puppy to learn to be confident.
Do not fall into the trap of thinking that one interaction with one event is enough. Pair these events with wonderful treats and your puppy will enjoy the events. Think of a fire engine as a socialization example. If your puppy hears the fire engine and then as it gets closer she gets treats, hopefully she will think in the future "I hope that noise happens again, I get treats when that happens!" That is the goal to have your dog happily anticipate something wonderful as a result of another event happening. If you give your dog steak every time he sees the mailman, your dog will LOVE the mailman! So, what can you do to socialize your puppy properly in a cold weather city with the “socialization clock ticking?â€
Here are some suggestions for you:
- Take your puppy to dog-friendly establishments with a pocketful of treats. Everyone time your puppy comes into contact with someone, she should get a treat. You can give the treats, or even better, give treats to the person that you meet to give to your puppy.
- Have "puppy socialization parties" and invite your friends over. Ask them to bring big hats, glasses, Halloween costumes, baggy coats, wigs, and umbrellas. Everyone should give your puppy treats while wearing their various clothing items.
- Bring out warm weather items such as inline skates and wear them in front of your puppy and give her treats.
- Take your puppy to a good, positive reinforcement puppy class.
- Don't stop socializing your puppy after the socialization period. Research indicates that dogs need continued socialization well past their initial socialization.
- Play sound cds at a low level and pair with treats. Examples include thunderstorms, truck noises, baby noises, etc.
- Practice daily handling exercises with your puppy daily and pair the experience with treats. Handling examples include gently pulling ears, rubbing paws, and brushing teeth.
- Get your puppy used to people playing with her food or approaching her food bowl or bones while she is eating. Food aggression or resource guarding can happen if your dog is not comfortable with people around her food.
- Introduce your puppy safely to lots and lots of kids.
- Introduce your puppy to unusual sights such as elevator doors opening, crowds of people, big hats, snow blowers, moving shovels and anything else that is new. Pair each greeting with wonderful treats.
- Practice "proactive" socialization. Do not wait until your puppy is reacting to a stimulus. The stimulus should not have any effect on your puppy and then she should get a treat.
- If your puppy reacts to something or stops taking treats, move away to a location where she will take treats again.
Focus on socialization now and you can improve the chances that your puppy will grow up to be a confident, wonderful dog that you can bring with you anywhere. 

Think of socialization as an investment. Put the time in now and it will pay off for years and years!